1. Field of the Invention
This invention relates to a method of and a system for controlling an ignition timing retard limit in an internal combustion engine ignition control apparatus, and more particularly to improvement in a method of and a system for controlling an ignition timing retard limit suitable for use in an a motor vehicle having an electronic controlled engine ignition timing control system, seeking ignition timing from an intake air flowrate and an engine speed, and comparing the ignition timing with the retard limit to prevent the ignition timing from being on the retard side beyond the retard limit.
2. Description of the Prior Art
Heretofore, it has been known that, in a spark-ignition internal combustion engine, the ignition timing is closely related to the output performance and fuel consumption performance of the engine. Consequently, there has been put in practical use a so-called electronic controlled ignition timing control system, wherein, in order to steadily control to the optimal ignition timing in accordance with the operating conditions of the engine, the ignition timing is sought from an engine load such as an intake air flowrate and an engine speed to control the actual ignition timing for obtaining the optimal ignition timing.
In the electronic controlled ignition timing control system of the type described, when the engine load is detected from the intake air flowrate, an air flow meter of flap type generally is used to measure the intake air flowrate. With the air flow meter of this flap type, a measured flowrate of intake air excessively larger than the actual flowrate of intake air can occur after the rapid opening operation of a throttle valve due to the increase in the flowrate of intake air during rapid acceleration. In the aforesaid electronic controlled ignition timing control system, generally the higher side of load, where the measured flowrate of intake air is increased, is selected, the more the ignition timing is retarded. Hence, there exits in such prior art systems the disadvantage that the ignition timing is temporarily over-retarded due to the above phenomenon, whereby the output performance becomes insufficient and the fuel consumption performance is deteriorated.
To obviate the above-described disadvantages, there has been proposed to temporarily advance the ignition timing after rapid acceleration. However, since it is necessary to avoid knocking immediately after the acceleration, the control operations have to be able to compensate for the fact that the ignition timing can be over-advanced after the measured flowrate of intake air has come into agreement with the actual flow rate, thus presenting a possibility of causing knocking.